Sunday, December 8, 2019

Significant "additional" cooling after snowfall event depends on the type of snowflakes

~Refraction method observed in the Arctic revealed an important facet with respect to after snowfall surface temperatures.
~The method confirms that T*** top of snow temperature is colder when the snow layer snowflakes are larger.
~ This lingered well afterwards even when the clouds persisted,  a quite specific and peculiar key observation
~In this situation of bigger snowflakes within the carpet, when the clouds clear even a little,  surface temperatures dropped really fast, only to warm quickly as soon as cloudier not necessarily overcast conditions returned.

   During the Arctic long night we have the luxury of darkness eliminating sun ray heat effects.  After a period of  unusually large snow flakes we can literally precisely measure if different flakes cause temperature variations. Unlike snow beds in sunnier climes,   most flakes remain buried in place for the duration of winter,  as long as from October till June.  When the precipitation occurred,   Resolute Bay  October 2019 was likely the warmest in history,  it was mainly extensively cloudy and so with clouds there was very little chance for the  usual cooling clear skies triggering the start of winter.  Hence,  beginning of October had a lot of snow usually called "wet",  they  create a weaker density layer, compact less in the winds as can ice crystals or very small "colder" snowflakes do.   After weeks on ground, they are only readily identifiable by walking over the snow pack, causing while walking intense sinking with every step.   Measuring T*** with high precision thermistor revealed a marked cooling as compared with previous years.  Onto itself this cooling can affect the local refraction horizon and it did:

Twice confirmed,  with 2018 in blue,  2019 in red.  Top 2 bars, the average local horizon height was significantly higher in 2019 compared to 2018 same period.  2nd series from top, the average temperature difference between surface temperature (Ts) and top of snow layer (T***)  was greater in 2019 by +0.4 C.  3rd group down, average temperature readings at 2 meter height was colder in 2019 than 2018.  Finally bottom bars average T*** in 2019 was equally colder than 2018.   Measurements were done between October 5 and November 30 2019.  Greater sublimation of snow is the suspected causation.

      To sum it up,  the greater the positive temperature difference between Ts and T*** ,  the stronger the refraction,  observed by the horizon mainly appearing higher.  In other words,  a "wetter" snow bed causes more sublimation,  hence steeper cooling at the interface between snow and air.   Remember this sublimation cooling occurred in the Arctic long night, no sun, solar rays would exacerbate the sublimation,  which infers much more cooling.     The temperatures taken, with respect to the graph above were done nearly simultaneously with the refraction observations.  This is important, these temperatures are not daily averages,  which would require 24 near simultaneous refraction observations.

    A very difficult observation is to contrast top of drift snow pack (left) with 30 cm below (right).  The  bottom snow layers are much less dense.   But appear the same in a cross section scope,  however placed on a slab with 5X magnification the top layer primarily appears as  ice crystals while
the bottom "wet" snow in origin semi compacted has fewer ice crystals.  Yet the best way
to judge the differing layers is to simply walk on snow, usually a well compacted snow carpet leaves a very shallow footprint as opposed to a less dense one,  the former is like walking on concrete,  the latter causes difficulty in walking.  WD December  8 2019. 

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